[TableGen] Print a warning when a Processor contains duplicate Features / TuneFeatures (#137864)

I don't think a processor should normally contains duplicate features. This patch prints a warning whenever that happens in either the features or tune features.

Author: mshockwave

llvm/test/TableGen/DuplicateProcessorFeatures.td

@@ -0,0 +1,17 @@
+// RUN: llvm-tblgen -gen-subtarget -I %p/../../include %s 2>&1 | FileCheck %s
+
+include "llvm/Target/Target.td"
+
+def MyTarget : Target;
+
+def FeatureA : SubtargetFeature<"NameA", "", "", "">;
+def FeatureB : SubtargetFeature<"NameB", "", "", "">;
+def FeatureC : SubtargetFeature<"NameC", "", "", "">;
+
+// CHECK: warning: Processor CPU0 contains duplicate feature 'NameA'
+def P0 : ProcessorModel<"CPU0", NoSchedModel, [FeatureA, FeatureB, FeatureA]>;
+// CHECK: warning: Processor CPU1 contains duplicate tune feature 'NameB'
+// CHECK: warning: Processor CPU1 has 'NameC' in both feature and tune feature sets
+def P1 : ProcessorModel<"CPU1", NoSchedModel,
+                        /*Features=*/[FeatureC],
+                        /*TuneFeatures=*/[FeatureB, FeatureB, FeatureC]>;

llvm/utils/TableGen/SubtargetEmitter.cpp

@@ -333,6 +333,30 @@ unsigned SubtargetEmitter::cpuNames(raw_ostream &OS) {
   return Names.size();
 }
 
+static void checkDuplicateCPUFeatures(StringRef CPUName,
+                                      ArrayRef<const Record *> Features,
+                                      ArrayRef<const Record *> TuneFeatures) {
+  // We have made sure each SubtargetFeature Record has a unique name, so we can
+  // simply use pointer sets here.
+  SmallPtrSet<const Record *, 8> FeatureSet, TuneFeatureSet;
+  for (const auto *FeatureRec : Features) {
+    if (!FeatureSet.insert(FeatureRec).second)
+      PrintWarning("Processor " + CPUName + " contains duplicate feature '" +
+                   FeatureRec->getValueAsString("Name") + "'");
+  }
+
+  for (const auto *TuneFeatureRec : TuneFeatures) {
+    if (!TuneFeatureSet.insert(TuneFeatureRec).second)
+      PrintWarning("Processor " + CPUName +
+                   " contains duplicate tune feature '" +
+                   TuneFeatureRec->getValueAsString("Name") + "'");
+    if (FeatureSet.contains(TuneFeatureRec))
+      PrintWarning("Processor " + CPUName + " has '" +
+                   TuneFeatureRec->getValueAsString("Name") +
+                   "' in both feature and tune feature sets");
+  }
+}
+
 //
 // CPUKeyValues - Emit data of all the subtarget processors.  Used by command
 // line.
@@ -360,6 +384,10 @@ unsigned SubtargetEmitter::cpuKeyValues(raw_ostream &OS,
     ConstRecVec TuneFeatureList =
         Processor->getValueAsListOfDefs("TuneFeatures");
 
+    // Warn the user if there are duplicate processor features or tune
+    // features.
+    checkDuplicateCPUFeatures(Name, FeatureList, TuneFeatureList);
+
     // Emit as "{ "cpu", "description", 0, { f1 , f2 , ... fn } },".
     OS << " { "
        << "\"" << Name << "\", ";